The invention relates to a method and to a receiver device for reconstructing signals distorted by multipath propagation.
In radio systems, in particular mobile radio systems or wireless communication systems, the increasing numbers of subscribers is leading to difficulties when received signals are to be assigned to the signal sources transmitting the signals and the signals are to be reconstructed.
When they propagate through a propagation medium, signals suffer interference from noise. As a result of diffraction and reflection, signal components travel along different propagation paths between the signal source and the signal destination, are superposed at the signal destination and cause cancellation effects there. In addition, when there are a plurality of signal sources, the signals from different signal sources become superposed. Frequency multiplexing, time-division multiplexing or a method known as code division multiplexing use frequency, time-slot or code allocation to each subscriber--that is to say to each signal source while the subscriber is transmitting--and can therefore discriminate between the subscribers in a radio network cell. By these measures, it is also possible to reconstruct signals with multipath propagation. However, difficulties arise in coping with the increasing numbers of subscribers within the constraints of the physical transmission conditions.
A. J. van der Veen, P. B. Ober and E. F. Deprettere, "Azimuth and elevation computation in high resolution DOA estimation", IEEE Trans. Signal Processing, Vol.40, P.1828-1832, July 1992; R. Roy and T. Kailath, "ESPRIT--Estimation of signal parameters via rotational invariance techniques", IEEE Trans. Acoust., Speech, Signal Processing, Vol. ASSP-37, S.984-995, July 1989 and A. L. Swindlehurst and T. Kailath, "Azimuth/elevation direction finding using regular array geometries", IEEE Trans. Aerospace and Electronic Systems, Vol. 29, P. 145-156, January 1993 disclose methods for estimating the incidence directions of different signals at the signal destination. It is possible to determine the incidence direction independently of the chosen modulation methods or the chosen signal waveform, that is to say independently of other subscriber separation methods.
With the "Standard" ESPRIT method disclosed by R. Roy and T. Kailath, "ESPRIT--Estimation of signal parameters via rotational invariance techniques", IEEE Trans. Acoust., Speech, Signal Processing, Vol. ASSP-37, P.984-995, July 1989, the signals can be reconstructed via the determined incidence direction if the signals reach the signal destination by single path propagation. However, in the case of multipath propagation, there is a substantially larger number of incident wavefronts, since a signal breaks down into signal components and these arrive physically as wavefronts at the signal destination via a plurality of propagation paths. The standard ESPRIT method cannot adequately process the wide variety of signal components due, for example, to reflections, and is therefore unsuitable for applications involving multipath propagation of the signals.
Each of German reference DE 30 06 451 A1, U.S. Pat. No. 4,736,460 and U.S. Pat. No. 4, 989,262 disclose further circuit arrangements for interference cancellation. WO International reference 93/12590 discloses a method and a device for spatially separating signals which come from a plurality of signal sources and are transmitted simultaneously in the same frequency channel. In this case, the directional properties of the signal sources relative to the receiver (base station) are used for reconstructing the signals from the signal sources. However, only one signal component per signal is evaluated.